This invention relates to a method of making a nickel-coated copper substrate for use in a thin film composite and thin film composites containing such nickel-coated copper substrates.
In the past years, there have been extended efforts in the development of high capacitance electrochemical energy storage devices, especially capacitors and batteries, for use in reduced volumetric areas. Both capacitors and batteries store energy by the separation of positive and negative charges. The need to store greater amounts of energy in a smaller package continues to drive new research
Energy storage devices made of thin film composites have been found to be useful in electronic and optoelectronic applications, such as ferroelectric memory devices, pyroelectronic sensor devices, waveguide modulators, and acoustic sensors. For example, thin film composites are used in a variety of semiconductor integrated circuit devices such as analog circuits, rf circuits, and dynamic random access memories (DRAM""s).
The composites are usually composed of a substrate, a dielectric, and an electrode; the dielectric being between the substrate and the electrode. Substrates are commonly composed of copper, silicon, fused silica, platinum-coated silicon, alumina, sapphire, platinum-coated sapphire, or a single crystal SrTiO3 substrate.
Copper is often preferred as a substrate in light of its ready availability. Unfortunately, however, thin film composites having copper substrates often evidence thermal migration and outgassing. Thermal migration is the migration of copper ions into the dielectric and of ions in the dielectric into the substrate at elevated temperatures. Outgassing occurs when gaseous copper atoms escape from the substrate into either the dielectric or the oven in which deposition of the dielectric occurs. A copper substrate which eliminates these drawbacks is desired.
The invention relates to a method of preparing a copper substrate having nickel deposited thereon. In addition, the invention relates to thin film composites containing such nickel-coated copper substrates. The nickel-coated substrate is prepared by depositing nickel onto the copper and then annealing the resulting substrate. The copper may be a foil. After annealing, a dielectric may be deposited onto the substrate by methods known in the art such as by sol-gel or vacuum deposition techniques.